Start controlling method for a passenger protection system, start controlling system for a passenger protection system, and recording medium for recording a start controlling program for a passenger protection system

ABSTRACT

If deceleration in excess of a predetermined value is detected (step  104  in FIG.  2 ), a speed integral value ΔV as time integration of the deceleration is calculated (step  110  in FIG.  2 ). A segment length of a characteristic curve of the speed integral value ΔV in a predetermined range is calculated (steps  112, 114  in FIG.  2 ). If it is decided that the segment length is smaller than a predetermined value l 2  (step  116  in FIG.  2 ), the crash is decided as the low speed crash, etc. other than a soft crash. An air bag is inflated if the speed integral value ΔV exceeds a predetermined threshold value V TH , whereas the speed integral value ΔV is incremented by a predetermined value α (step  118  in FIG.  2 ) if it is decided that the segment length exceeds l 2  (step  116  in FIG.  2 ). Then, if it is decided that the speed integral value ΔV exceeds the threshold value V TH  ( step  112  in FIG.  2 ), inflation of the air bag is executed to detect generation of the soft crash.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to control of a passengerprotection system for protecting passengers in a car crash and, moreparticularly, a start controlling method for a passenger protectionsystem and a start controlling system for a passenger protection systemboth are able to distinguish between a low speed clash and a soft crash,and a recording medium for recording a start controlling program for apassenger protection system.

[0003] 2. Description of the Related Art

[0004] In the prior art, it has been well known that, according to therunning speed and the crashed part of the vehicle, type of crash of thevehicle is classified into a low speed frontal crash wherein an entirefrontal area of the vehicle collides with an object at low speed, a highspeed frontal (head-on) crash wherein the entire frontal area of thevehicle collides with the object at high speed, a high speed offsetcrash wherein a part of the entire frontal area of the vehicle collideswith the object at high speed, and others.

[0005] In a passenger protection system represented by an air bagsystem, for example, which can protect a body of the passenger in suchcrash, normally it is designed that such start control should beexecuted by taking account of difference in the acceleration of thevehicle in crash from that in normal running. Various start controllingmethods and systems for embodying the same, etc. have been proposed upto now.

[0006] A following concept has been proposed as one of start controlconcepts for the passenger protection system which has been proposeduntil now. In other words, at first the integral value (speed integralvalue) of the deceleration (so-called impact acceleration) upon crash iscalculated. Then, it is decided whether or not change in the integralvalue within a predetermined range is continued on over a predeterminedperiod of time, i.e., it is decided whether or not stagnation of theintegral value is caused. If it has been decided that the stagnation ofthe integral value is caused, a predetermined value is then added to theintegral value. Therefore, the integrated value is advanced rather thanthe actual integral value, and then start of the air bag is carried outwhen it is decided that the integrated value has exceeded apredetermined threshold value.

[0007] In the meanwhile, while taking account of the stagnation of thespeed integral value which is caused in the crash which is generallycalled as a soft crash such as an oblique crash, an offset crash, a polecrash, etc., the above start controlling method has been proposed tostart the air bag without fail, while distinguishing between the softcrash and the high speed crash in which no stagnation of the speedintegral value is caused, etc. However, such start controlling methodhas not been satisfactory in the following respects and therefore hasnot been employed in practical use.

[0008] More particularly, there has been the low speed crash as the casewhere start of the air bag is not needed. In such low speed crash,change in the speed integral value of the impact acceleration has thestagnation of the speed integral value, like the above-mentioned softcrash. In addition, sometimes a stagnation time of the speed integralvalue in the low speed crash is close or resemble to that in the softcrash. Therefore, in some cases there has been a possibility thatdistinctions between the soft crash and the low speed crash becomedifficult according to the above concept.

SUMMARY OF THE INVENTION

[0009] The present invention has been made in view of the abovecircumstances, and it is an object of the present invention to provide astart controlling method for a passenger protection system which issuited for practical use and a system for embodying the same, and arecording medium for recording a start controlling program for apassenger protection system.

[0010] It is another object of the present invention to provide a startcontrolling method for a passenger protection system which is able todistinguish between a soft crash and a low speed crash to thus achievehigher practicality and a system for embodying the same, and a recordingmedium for recording a start controlling program for a passengerprotection system.

[0011] In order to achieve the above objects of the present invention,according to a first aspect of the present invention, there is provideda start controlling method for a passenger protection system, ofcontrolling start of the passenger protection system which isconstructed such that a protection system for protecting passengers in avehicle is started in response to a start signal supplied from anexternal device, comprising the steps of:

[0012] executing integral of deceleration of a vehicle with respect totime;

[0013] calculating a segment length of change in an integral value in apredetermined range of the integral value, which is derived by theintegral of time, relative to an elapsed time; and

[0014] deciding type of crash by comparing a calculated value of thesegment length with a reference value.

[0015] Such start controlling method is made based on a followingviewpoint. That is, based on the result of study achieved by inventorsof the present invention, the stagnation of the integral value is causedin a certain interval of change in the speed integral value asintegration of the deceleration with respect to time according to typeof crash, but the segment length of the integral value relative to theelapsed time becomes different according to the type of crash even inthe case where such stagnation of the integral value is caused, so thatthe type of crash can be distinguished from each other based on thedifference in the segment length.

[0016] It is preferable that, when the segment length is to becalculated, the predetermined range of the integral value should bedefined by a point of start of the stagnation of the integral value,i.e., the integral value at a start point, and a point of termination ofthe stagnation of the integral value, i.e., the integral value at an endpoint. In practice, it is preferable that, since the values aredifferent according to type of the vehicle, etc., such values should beset based on experimental data, or set by taking account of variousconditions, etc. as well as experimental data.

[0017] More particularly, the present invention is suitable fordistinction between the so-called soft crash such as an oblique crash, apole crash, etc., which needs start of the passenger protection system,and the low speed crash, which does not need start of the passengerprotection system.

[0018] Therefore, it is preferable that the above reference value shouldbe set to the segment length of change in the integral value in apredetermined range of the integral value, which is derived by theintegral of time of the deceleration of the vehicle in a low speedcrash, relative to the elapsed time, and type of crash should be decidedas the soft crash if the segment length which is larger than thereference value has been calculated.

[0019] In order to achieve the above objects of the present invention,according to a second aspect of the present invention, there is provideda start controlling system for a passenger protection system, forcontrolling start of the passenger protection system which isconstructed such that a protection system for protecting passengers in avehicle is started in response to a start signal supplied from anexternal device, comprising:

[0020] a deceleration deciding means for deciding whether or notdeceleration which is input from an external means exceeds apredetermined magnitude;

[0021] an integrating means for executing integral of time of thedeceleration which is input from the external means to calculate a speedintegral value if it has been decided by the deceleration deciding meansthat the deceleration exceeds the predetermined magnitude;

[0022] a segment length calculating means for calculating a segmentlength in a predetermined range of the speed integral value which iscalculated by the integrating means, relative to an elapsed time;

[0023] a segment length deciding means for deciding whether or not thesegment length which has been calculated by the segment lengthcalculating means exceeds a predetermined value;

[0024] an incrementing means for adding a predetermined increment valueto the speed integral value at that point of time if it has been decidedby the segment length deciding means that the segment length which hasbeen calculated by the segment length calculating means exceeds thepredetermined value; and

[0025] a decision starting means for generating a start signal for thepassenger protection system if it has been decided that a value derivedby the incrementing means exceeds a predetermined threshold value.

[0026] Such configuration is implemented by the start controlling methodset forth in claim 1 so as to enable the start of the passengerprotection system. The deceleration deciding means, the integratingmeans, the segment length calculating means, the segment length decidingmeans, the incrementing means, and the decision starting means can beimplemented by causing the so-called CPU, which has a function of acomputer, to execute the predetermined program.

[0027] It is preferable that, when the segment length is to becalculated, the predetermined range of the integral value should bedefined by a point of start of the stagnation of the integral value,i.e., the integral value at a start point, and a point of termination ofthe stagnation of the integral value, i.e., the integral value at an endpoint. In practice, it is preferable that, since the values aredifferent according to type of the vehicle, etc., such values should beset based on experimental data, or set by taking account of variousconditions, etc. as well as experimental data.

[0028] In addition, the decision starting means may be composed of athreshold value deciding means for deciding whether or not a valuederived by the incrementing means exceeds a predetermined thresholdvalue, and a start signal generating means for generating a start signalfor the passenger protection system if it has been decided by thethreshold value deciding means that the value derived by theincrementing means exceeds the predetermined threshold value.

[0029] In order to achieve the above objects of the present invention,according to a third aspect of the present invention, there is provideda start controlling system for a passenger protection system, forcontrolling start of the passenger protection system which isconstructed such that a protection system for protecting passengers in avehicle is started in response to a start signal supplied from anexternal device, comprising:

[0030] a central processing unit for reading a predetermined programfrom another external device and then executing predetermined processesby executing the predetermined program;

[0031] a memory device for storing a program which is to be executed bythe central processing unit in such a manner that the program can beread by the central processing unit;

[0032] a digital/analogue converter for converting a digital startsignal, which is supplied from the central processing unit to an air bagsystem, into an analogue signal; and

[0033] an interface circuit for converting an output signal of thedigital/analogue converter into a predetermined signal which is suitedfor the air bag system;

[0034] wherein the central processing unit

[0035] executes integral of time of deceleration of the vehicle, whichis input from an external means,

[0036] calculates a segment length of change in an integral value in apredetermined range of the integral value, which is derived by theintegral of time, relative to an elapsed time,

[0037] compares a calculated value of the segment length with areference value which is the segment length of change in the integralvalue in a predetermined range of the integral value, which is derivedby the integral of time of the deceleration of the vehicle in a lowspeed crash, relative to the elapsed time,

[0038] decides that type of crash is a soft crash if it has been decidedthat the calculated value of the segment length is larger than thereference value,

[0039] decides whether or not a speed integral value exceeds apredetermined threshold value if it has been decided that the type ofcrash is the soft crash, and

[0040] outputs a start signal of an air bag system if it has beendecided that the speed integral value exceeds the predeterminedthreshold value.

[0041] In order to achieve the above objects of the present invention,according to a fourth aspect of the present invention, there is provideda recording medium for recording a plurality of computer-readableinstructions, comprising:

[0042] a first instruction means for causing a computer to decidewhether or not deceleration which is input from an external meansexceeds a predetermined magnitude;

[0043] a second instruction means for causing the computer to executeintegral of time of the deceleration to calculate a speed integral valueif it has been decided that the deceleration which is input from theexternal means exceeds the predetermined magnitude;

[0044] a third instruction means for causing the computer to calculate asegment length in a predetermined range of the speed integral valuebeing calculated, relative to an elapsed time;

[0045] a fourth instruction means for causing the computer to decidewhether or not the segment length being calculated exceeds apredetermined value;

[0046] a fifth instruction means for causing the computer to add apredetermined increment value to the speed integral value at that pointof time if it has been decided that the segment length being calculatedexceeds the predetermined value;

[0047] a sixth instruction means for causing the computer to decidewhether or not the speed integral value, to which the predeterminedincrement value is added, exceeds a predetermined threshold value; and

[0048] a seventh instruction means for causing the computer to generatea start signal to start a passenger protection system if it has beendecided that the speed integral value exceeds the predeterminedthreshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049]FIG. 1 is a schematic block diagram showing a configuration of astart controlling method for a passenger protection system according toan embodiment of the present invention;

[0050]FIG. 2 is a flowchart showing procedures in start control carriedout by the start controlling method for the passenger protection systemshown in FIG. 1;

[0051]FIGS. 3A and 3B are views showing a characteristic curve of changein deceleration and its integral of time value in a soft crashrespectively, wherein FIG. 3A is a characteristic curve showing changein the deceleration relative to an elapsed time, and FIG. 3B is acharacteristic curve showing change in integral of time of thedeceleration shown in FIG. 3A relative to the elapsed time;

[0052]FIGS. 4A and 4B are views showing a characteristic curve of changein deceleration and its integral of time value in a low speed crashrespectively, wherein FIG. 4A is a characteristic curve showing changein the deceleration relative to the elapsed time, and FIG. 4B is acharacteristic curve showing change in integral of time of thedeceleration shown in FIG. 4A relative to the elapsed time;

[0053]FIG. 5 is a graph showing a concrete example of an incrementvariable α which is to be added to a speed integral value; and

[0054]FIG. 6 is a schematic view showing a configuration of a startcontrolling system for a passenger protection system when a floppy diskis employed to load a program.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Preferred embodiments of the present invention will be explainedin detail with reference to the accompanying drawings hereinafter.

[0056] Members, arrangements, etc. described in the following should beinterpreted not to limit the present invention, and therefore they maybe varied or modified variously in the range of the gist of the presentinvention.

[0057] At first, a basic configuration of a start controlling system fora passenger protection system according to an embodiment of the presentinvention (referred to as the “present system” hereinafter) will beexplained with reference to FIG. 1 hereinbelow.

[0058] As shown in FIG. 1, a hardware configuration of the presentsystem S comprises a first interface circuit (labeled as an “I/F(1)” inFIG. 1) 1, an analogue/digital converter (labeled as an “A/D” in FIG. 1)2 for converting an analogue signal into a digital signal, a ROM (ReadOnly Memory) 3, a central processing unit (labeled as a “CPU” in FIG. 1)4, a RAM (Random Access Memory) 5, a digital/analogue converter (labeledas an “D/A” in FIG. 1) 6 for converting a digital signal into ananalogue signal, and a second interface circuit (labeled as an “I/F(2)”in FIG. 1) 7. As described later, the present system S is constructed tocontrol start of an air bag system 9 acting as the passenger protectionsystem, based on acceleration detected by an acceleration sensor 8 upona car crash (i.e., deceleration).

[0059] The first interface circuit 1 executes a level conversion of asignal being input from the acceleration sensor 8. An output signal ofthe first interface circuit 1 is converted into the digital signal bythe analogue/digital converter 2 and then input into the centralprocessing unit 4.

[0060] The ROM 3 is a well known IC memory device which is employed onlyto read data. The program, constants, etc. which are employed toimplement a start controlling operation described later are stored inadvance in this ROM 3.

[0061] The central processing unit 4 controls an overall operation ofthe present system S described later. For example, the centralprocessing unit 4 is constructed to employ a well known IC microcomputer(CPU). In place of the CPU, a DSP (Digital Signal Processor) which iswell known as an integrated circuit to make high speed processingpossible may be employed.

[0062] The RAM 5 is a well known IC memory device which is employed tostore/read results of arithmetic operations performed by the centralprocessing unit 4, etc.

[0063] The second interface circuit 7 acts as an interface between thepresent system S and the air bag system 9. More particularly, when thedigital start signal which is output from the central processing unit 4is converted into the analogue signal by the digital/analogue converter6 and then the analogue signal is input into the second interfacecircuit 7, various processes, e.g., signal level conversion of theanalogue signal to be fit for the air bag system 9, are conducted by thesecond interface circuit 7 and then such analogue signal is output tothe air bag system 9.

[0064] As the typical acceleration sensor, there are a semiconductoracceleration sensor, a piezo-electric acceleration sensor, etc. Theacceleration sensor 8 of the present system S should not be limited to aparticular type acceleration sensor, and any type acceleration sensormay be employed in the present invention.

[0065] The air bag system 9 is a well known one which consists of aninflator (gas generator) (not shown) and an air bag main body. The airbag system 9 is constructed such that, when the start signal is inputfrom the present system S, a gas is generated by the inflator to inflatethe air bag main body.

[0066] Next, procedures in start control carried out by the centralprocessing unit 4 will be explained with reference to FIG. 2 hereunder.

[0067] When an operation of the central processing unit 4 is started, atfirst various variables, flags, etc. are initialized (see step 100 inFIG. 2).

[0068] The deceleration G detected by the acceleration sensor 8 is theninput (see step 102 in FIG. 2). It is then decided whether or not thedeceleration G exceeds predetermined deceleration Go (see step 104 inFIG. 2).

[0069] The predetermined deceleration Go is set to a value of thedeceleration which is not generated in a normal running state of thevehicle. For example, the predetermined deceleration Go is decided bytaking account of various empirical conditions as well as experimentaldata. The deceleration G has a negative value. Such deceleration G isincreased larger to the negative side as impact caused by the crash isenhanced stronger. Therefore, in the embodiment of the presentinvention, the meaning of “the deceleration G is increased” is “thedeceleration G has a more negative value”, i.e., “an absolute value ofthe deceleration G is increased”.

[0070] Assume that the deceleration G and the deceleration Go have theabsolute value respectively in an inequality G>Go in step 104.

[0071] In step 104, if it has been decided that G>Go (if YES), i.e., ifit has been decided that the deceleration G is larger than thepredetermined deceleration Go, the process goes to step 110 describedlater. In contrast, unless it has been decided that the deceleration Gis larger than the predetermined deceleration Go (if NO), i.e., if ithas been decided that the deceleration which is regarded as the crashhas not been generated yet, then it is decided whether or notintegration process (see step 110 in FIG. 2) described later has alreadybeen started (see step 106 in FIG. 2).

[0072] In step 106, if it has been decided that the integration processhas not been started yet (if NO), the process returns to above step 102since the deceleration has not come up to such a state that it isregarded as the crash.

[0073] On the contrary, in step 106, if it has been decided that theintegration process has already been started (if YES), then it isdecided whether or not a speed integral value ΔV which is a integral oftime value of the deceleration is larger than a predetermined value −V3(see step 108 in FIG. 2).

[0074] Then, if it has been decided that the speed integral value ΔV islarger than the predetermined value −V3, i.e., if it has been decidedthat the speed integral value ΔV has a value more close to the positiveside than the predetermined value −V3 (if YES), the process returns tostep 100 since there is no need to start the air bag system. Then, aseries of processes are started newly (see step 108 in FIG. 2).

[0075] In this case, the predetermined value −V3 is selected to suchextent that the vehicle is not brought into a state wherein the air bagsystem 9 must be started and thus the vehicle is able to run withouttrouble. Thus, the predetermined value −V3 may be set experimentally orset by adding various conditions to experimental data. For example, inFIG. 4A, a characteristic curve showing change in the decelerationrelative to the elapsed time in low speed crash is depicted. In FIG. 4B,a characteristic curve showing change in the integral of time value ofthe deceleration relative to the elapsed time is depicted. Thepredetermined value −V3 will be explained with reference to FIGS. 4A and4B in the following.

[0076] In FIG. 4B, as described later, values −V1 and −V2 are levels ofthe speed integral value ΔV which is one of references to decide a lowspeed crash in this start control. The above value −V3 is set to a levelsmaller than these values −V1 and −V2 (in other words, set to a valuemore close to the positive side) (see FIG. 4B).

[0077] In contrast, in step 108, if it has been decided that ΔV>−V3 isnot satisfied (if NO), i.e., if it has been decided that the speedintegral value ΔV has the more negative side value than the value −V3,the process advances to step 110. Then, in step 110, the speed integralvalue ΔV is calculated by integrating the deceleration G, which is inputby the process in step 102, with respect to time (see step 110 in FIG.2).

[0078] Then, it is decided whether or not the calculated speed integralvalue ΔV is suppressed within a predetermined range (see step 112 inFIG. 2). More particularly, it is then decided whether or not aninequality −V2>ΔV>−V1 is satisfied.

[0079] Next, the principle of the start controlling method in theembodiment of the present invention as well as respective meanings of−V1 and −V2 in the above inequality will be explained with reference toFIGS. 3A and 3B and FIGS. 4A and 4B hereunder.

[0080] The start controlling method in the embodiment of the presentinvention is constructed such that it is able to distinguish the type ofcrash which needs the start of the air bag system 9 and which is calledgenerally as a soft crash, and the low speed crash which does not needthe start of the air bag system 9. In the soft crash such as an obliquecrash, an offset crash, a pole crash, etc., stagnation is caused in thespeed integral value. In particular, the start controlling method in theembodiment makes it possible to distinguish the soft crash and the lowspeed crash by taking notice of a respect described in the following.

[0081] In the prior art, as one of the concepts of the start control ofthe air bag system against the soft crash, there has been start controlwhich is decided based on whether or not the stagnation is caused in thespeed integral value ΔV.

[0082] In other words, in FIGS. 3A and 3B, change in the deceleration inthe soft crash and a typical example of the speed integral value ΔVwhich is the integral of time value of the change in the decelerationare shown respectively. In the case of the soft crash, as shown in FIG.3A, in most cases the decelerations are generated successively at arelatively small level (see a time interval indicated by a reference ain FIG. 3A) and then the relatively large deceleration which has aplurality of peaks is caused. Then, as shown in FIG. 3B, the speedintegral value ΔV is relatively loosely changed in a time interval whichcorresponds to the above time interval indicated by the reference +E,unsa to thus cause the stagnation of the speed integral value ΔV. Then,change in the speed integral value ΔV is also enhanced in response toappearance of the relatively large deceleration (see FIG. 3A).

[0083] For this reason, in the prior art, there has been the followingconcept of start control with regard to such change in the speedintegral value ΔV. That is, a period of time which is required for thespeed integral value ΔV to pass through the predetermined value −V2 andthen come up to the predetermined value −V1 is detected. If the timeexceeds a predetermined period of time ta, the type of crash is decidedas the soft crash. Thus, a predetermined value is added to the speedintegral value ΔV (a characteristic curve indicated by a broken line inFIG. 3A represents the speed integral value after the addition has beenexecuted) so as to make the speed integral value ΔV exceed positively athreshold value V_(TH). Where the predetermined value −V2 is a speedintegral value which substantially corresponds to a start point of thetime interval during when the deceleration of relatively small level issuccessively generated, as indicated by the reference +E,uns a in FIG.3A, for example, and the predetermined value −V1 is a speed integralvalue which substantially corresponds to an end point of the above timeinterval. That is to say, the predetermined value −V2 is an integralvalue at a point of start, i.e., a start point of the stagnation of theintegral value, while the predetermined value −V1 is an integral valueat a point of termination, i.e., an end point of the stagnation of theintegral value.

[0084] However, in the start control in the prior art, there has been apossibility that a disadvantage is caused as described in the following.

[0085] More particularly, in the low speed crash, as the representativeexample is shown in FIG. 4A, the deceleration seldom has a peak andbecomes continuous around a certain level. But, as shown in FIG. 4B, thestagnation is caused in the integral of time value of the deceleration,like the case of the above-mentioned soft crash. In addition, a periodof time tb, which is required for the speed integral value ΔV to passthrough from the predetermined value −V2 to −V1, tends to have a valuerelatively similar to the predetermined period of time ta in the case ofthe above soft crash.

[0086] Therefore, in the event of the above-mentioned concept of startcontrol, the low speed crash cannot be distinguished from the soft crasheven if such low speed crash which does not need inflation of the airbag is caused. As a result, there is a possibility of bringing about thestart of the air bag. Therefore, the above start control in the priorart has not been employed in practical use.

[0087] As the result of earnest study to find differences in changes inthe deceleration, the speed integral value, etc. between the soft crashand the low speed crash, the inventors of the present invention havecome to the conclusion that the soft crash and the low speed crash canbe distinguished from each other, based on difference in segment lengthsof the characteristic curve showing the change in the speed integralvalue. Thus, the start controlling method in the embodiment of thepresent invention is made based on such viewpoint.

[0088] More specifically, as for the change in the speed integral valuein the soft crash and the low speed crash, if changes in respectivecharacteristic curves are compared with each other within apredetermined same range, e.g., the range of the speed integral valuefrom −V2 to −V1 in FIGS. 3B and 4B respectively, the speed integralvalue ΔV is directed to −V1 relatively smoothly with the elapsed time inthe low speed crash, whereas the speed integral value ΔV is directed to−V1 with variation of the integral value in the soft crash. In otherwords, it is possible to say that the segment length of the speedintegral value from −V2 to −V1 in the soft crash becomes long ratherthan that in the low speed crash. Therefore, the start controllingmethod in the passenger protection system according to the presentinvention can distinguish between the soft crash and the low speed crashaccording to such difference in the segment length of the characteristiccurve of the speed integral value within the predetermined range, andthus can provide a more practical start controlling method than theprior art.

[0089] Returning to FIG. 2 again, if it has been decided in step 112that the inequality −V2>ΔV>−V1 is satisfied (if YES), the segment lengthis calculated in the predetermined range from −V2 to −V1 (see step 114in FIG. 2).

[0090] More specifically, for example, if an infinitesimal segmentlength at a time t is assumed as ΔLt, first such infinitesimal segmentlength at a time t can be calculated as ΔLt={1+(ΔVt−ΔV_((t-1)))²}^(½).Where ΔVt is the speed integral value at a time t, and ΔV_((t−1)) is thespeed integral value at a time t−1 prior to the time t by apredetermined time (e.g., one clock of the CPU). Here assume that a timeinterval between ΔVt and ΔV_((t−1)) is enoughly small to be approximatedto 1, and a right-angled triangle has an oblique side of theinfinitesimal segment length ΔLt and two orthogonal sides of adifference between ΔVt and ΔV_((t−1)) and the time interval 1. Hence,this equation corresponds to calculate a length of the oblique side ofthe right-angled triangle. The segment length of the speed integralvalue from −V2 to −V1 can be calculated by integrating the infinitesimalsegment length ΔLt with respect to time. An interval of integration isthe time interval in which the speed integral value passes through −V2to come up to −V1.

[0091] After the segment length 1 has been calculated as describedabove, it is decided whether or not this segment length 1 is larger thana predetermined value l₂ (see step 116 in FIG. 2). Where the value l₂ isa segment length in the characteristic curve of the speed integral valuein the predetermined range of the speed integral value, i.e., the rangeof the speed integral value from −V2 to −V1 in the low speed crash (seeFIG. 4B). This value is set experimentally or set by adding variousconditions, etc. to experimental data. The value is stored previously inthe ROM 3 and then fetched by the central processing unit 4 as areference value in decision.

[0092] In step 116, if it has been decided that the segment length 1 isnot larger than the predetermined value l₂ (if NO), neither the softcrash nor the low speed crash is detected as the type of crash and thenthe process goes to step 120 described later. In contrast, if it hasbeen decided that the segment length 1 is larger than the predeterminedvalue l₂ (if YES), a value of an increment variable α is added to thespeed integral value ΔV at that point of time and then such added valueis set newly as the speed integral value ΔV at this point of time (seestep 118 in FIG. 2).

[0093] Where the increment variable α is set and added from a point ofview described in the following. That is, in decision whether or notinflation of the air bag is requested, as described later (see step 122in FIG. 2), since a threshold value employed to decide whether or notthe magnitude of the speed integral value reaches such a magnitude thatneeds inflation of the air bag is determined based on a high speedhead-on crash, the increment variable α is added to enable the speedintegral value ΔV to exceed the threshold value even in the soft crashwhich is the type of crash other than the high speed head-on crash. Thisincrement variable a is detected and set in advance experimentallyaccording to the type of vehicle. For example, as shown in FIG. 5, theincrement variable α is set to change stepwise based on the magnitude ofthe segment length calculated in step 114. In FIGS. 5, 1a, 1 b, and 1 care a segment length respectively in the characteristic curve of thespeed integral value from the point of time after the speed integralvalue ΔV has passed through the predetermined value −V2 (see FIG. 3B),and are appropriately set respectively.

[0094] In practice, values of the segment lengths and correspondingvalues α are tabulated as a conversion table based on the abovecharacteristic curve. Then, such conversion table is stored in a memory(not shown) in the central processing unit 4 or the ROM 3 previously tobe employed in step 118.

[0095] In this case, a portion of the characteristic curve indicated bythe broken line in FIG. 3B shows change in the speed integral value ΔVto which the increment variable α is added, as described above.

[0096] Then, if it has been decided in above step 112 that theinequality −V2>ΔV>−V1 is not satisfied (if NO), or if it has beendecided in above step 116 that the inequality 1>l₂ is not satisfied (ifNO), or if the above step 118 has been finished, then the thresholdvalue V_(TH) is decided in step 120.

[0097] In other words, the threshold value V_(TH) which is employed as areference value to decide whether or not the speed integral value ΔVreaches the magnitude to start the air bag system 9 is calculated byusing a previously set relation based on a magnitude of the decelerationG at this point of time, otherwise the threshold value V_(TH) is fetchedfrom a table in which relationships between the decelerations G and thethreshold values V_(TH), are stipulated and then set. In step 122,ΔV_(TH)=ΔV(G) means that ΔV_(TH) is a function of the deceleration G. Aconcrete relation between G and ΔV_(TH) is omitted herein. But, roughlyspeaking, according to the relation, for example, the level of thedeceleration G at which the air bag system 9 is started in the highspeed head-on crash is set based on simulation data derivedexperimentally or by the computer. An appropriate level of thedeceleration G is set every type of vehicle.

[0098] Then, it is decided whether or not the speed integral value ΔVexceeds the threshold value ΔV_(TH) being set as above (see step 122 inFIG. 2). If it has been decided that the speed integral value ΔV exceedsthe threshold value ΔV_(TH) (if YES), inflation of the air bag isneeded. Thus, the start signal is output from the central processingunit 4 to the air bag system 9 via the digital/analogue converter 6 andthe second interface circuit 7, so that the air bag is inflated (seestep 124 in FIG. 2).

[0099] On the contrary, in step 122, if it has been decided that thespeed integral value ΔV does not exceed the threshold value ΔV_(TH) (ifNO), the speed integral value ΔV does not come up to inflate the air bagand thus the process returns to above step 102. Then, as describedabove, a series of processes are repeated once again (see step 122 inFIG. 2).

[0100] In the above explanation, a deceleration deciding means can beimplemented by causing the central processing unit 4 to execute step 104shown in FIG. 2, an integrating means can be implemented by causing thecentral processing unit 4 to execute step 110 shown in FIG. 2, a segmentlength calculating means can be implemented by causing the centralprocessing unit 4 to execute step 114 shown in FIG. 2, a segment lengthdeciding means can be implemented by causing the central processing unit4 to execute step 116 shown in FIG. 2, an incrementing means can beimplemented by causing the central processing unit 4 to execute step 118shown in FIG. 2, and a decision starting means can be implemented bycausing the central processing unit 4 to execute steps 122, 124 shown inFIG. 2.

[0101] The decision starting means may consist of a threshold valuedeciding means and a start signal generating means. In this case, thethreshold value deciding means can be implemented by causing the centralprocessing unit 4 to execute step 112 shown in FIG. 2, and the startsignal generating means can be implemented by causing the centralprocessing unit 4 to execute step 124 shown in FIG. 2.

[0102] In the above explanation, the above start control is carried outon the premise that the program for executing the start control isstored in the ROM 3 previously. However, there is no necessity that theprogram should always be stored in the ROM 3 previously. That is to say,first the program is stored in the well known external storing medium,and then the central processing unit 4 can read the program from thisstoring medium when the start control is to be carried out.

[0103] In more detail, the magnetic recording medium such as a floppydisk, a hard disk, a magnetic tape, etc., an optical disk, and the like,for example, may be employed as such storing medium. Needless to say, itis a matter of course that, if such recording medium is employed, thesuitable reading device (e.g., the floppy disk drive, the hard diskdrive, or the like) must also be installed.

[0104] In FIG. 6, an example of a configuration of a start controllingsystem is shown in the case where the floppy disk 10 is employed as therecording medium for the program. A reading operation of the programwhen the floppy disk 10 is employed as the recording medium will beexplained with reference to FIG. 6 hereinbelow.

[0105] A floppy disk drive 11 is connected to the central processingunit 4. The program is loaded in advance onto the floppy disk 10. Theprogram can be fetched from the floppy disk 10 by operating the floppydisk drive 11, and then loaded onto the central processing unit 4, sothat the program is ready for use.

[0106] As described above, according to the present invention, since thestart controlling system is constructed to discriminate the differencein the segment length within the predetermined range of the elapsed timein the characteristic curve of the speed integral value as the timeintegration of the deceleration, respective types of crash can bediscriminated even in the type of crash in which the stagnation of thespeed integral value is caused.

[0107] Especially, in the invention set forth in claims 2, 6 and 9, thesoft crash and the low speed crash can be distinguished from each other,and therefore the start controlling method for the passenger protectionsystem and the system therefor, which is able to have high practicalitymore firmly than the prior art, and the recording medium for recordingthe start controlling program for the passenger protection system can beprovided.

What is claimed is:
 1. A start controlling method for controlling astart of a passenger protection system for protecting passengers in avehicle, the passenger protection system being started in response to astart signal, said start controlling method comprising: calculating aspeed integral value by integrating a deceleration of the vehicle withrespect to time; calculating a value of a segment length of change in anintegral value in a predetermined range of the speed integral valuerelative to an elapsed time; and deciding a type of crash by comparingthe value of the segment length with a reference value.
 2. A startcontrolling system for controlling a start of a passenger protectionsystem for protecting passengers in a vehicle, the passenger protectionsystem being started in response to a start signal, said startcontrolling system comprising: a deceleration deciding means fordeciding whether or not a deceleration of the vehicle exceeds apredetermined magnitude; an integrating means for integrating thedeceleration with respect to time to calculate a speed integral value ifit has been decided by said deceleration deciding means that thedeceleration exceeds the predetermined magnitude; a segment lengthcalculating means for calculating a value of a segment length of changein a predetermined range of the speed integral value relative to anelapsed time; a segment length deciding means for deciding whether ornot the value of the segment length exceeds a predetermined value; anincrementing means for adding a predetermined increment value to thespeed integral value at a point in time to derive a value if it has beendecided by the segment length deciding means that the value of thesegment length exceeds the predetermined value; and a decision startingmeans for generation the start signal for the passenger protectionsystem if the value derived by said incrementing means exceeds apredetermined threshold value.
 3. A start controlling system accordingto claim 2 , wherein said decision starting means comprises: a thresholdvalue deciding means for deciding whether or not the value derived bysaid incrementing means exceeds the predetermined threshold value; and astart signal generating means for generating the start signal for thepassenger protection system if it has been decided by said thresholdvalue deciding means that the value derived by said incrementing meansexceeds the predetermined threshold value.
 4. A start controlling systemaccording to claim 2 , wherein the predetermined value employed by saidsegment length deciding means is a segment length of change in anintegral value in a predetermined range of another speed integral value,the another speed integral value being derived from an integral of timeof deceleration of the vehicle in a low speed crash, relative to theelapsed time.
 5. A starting controlling system according to claim 3 ,wherein the predetermined value employed by said segment length decidingmeans is the segment length of change in an integral value in apredetermined range of another speed integral value, the another speedintegral value being derived from an integral of time of deceleration ofthe vehicle in a low speed crash, relative to the elapsed time.
 6. Astart controlling system for controlling a start of a passengerprotection system for protecting passengers in a vehicle, the passengerprotection system being started in response to a start signal, saidstart controlling system comprising: a central processing unit operableto: read a predetermined program and execute predetermined processes byexecuting the predetermined program, calculate a speed integral value byintegrating a deceleration of the vehicle with respect to time,calculate a value of a segment length of change in an integral value ina predetermined range of the speed integral value relative to an elapsedtime, compare the value of the segment length with a reference value,the reference value being a segment length of change in an integralvalue in a predetermined range of another speed integral value, theanother speed integral value being derived from an integral of time ofdeceleration of the vehicle in a low speed crash relative to the elapsedtime, decide that a type of crash is a soft crash if the value of thesegment length is larger than the reference value, decide whether or notthe speed integral value exceeds a predetermined threshold value if ithas been decided that the type of crash is the soft crash, and output adigital start signal for the passenger protection system if it has beendecided that the speed integral value exceeds the predeterminedthreshold value; a memory device operable to store a program to beexecuted by said central processing unit, such that the program can beread by said central processing unit; a digital/analogue converteroperable to convert the digital start signal supplied from said centralprocessing unit into an analogue signal; and an interface circuitoperable to convert the analogue signal from said digital/analogueconverter into a predetermined signal which is suited for the passengerprotection system.
 7. A computer program embodied on a computer readablemedium for use with a computer for controlling a start of a passengerprotection system for protecting passengers in a vehicle, said computerprogram comprising: computer readable program code operable to cause thecomputer to decide whether or not a deceleration exceeds a predeterminedmagnitude; computer readable program code operable to cause the computerto integrate the deceleration with respect to time to calculate a speedintegral value if it has been decided that the deceleration exceeds thepredetermined magnitude; computer readable program code operable tocause the computer to calculate a value of a segment length of anintegral value of change in a predetermined range of the speed integralvalue relative to an elapsed time; computer readable program codeoperable to cause the computer to decide whether or not the value of thesegment length exceeds a predetermined value; computer readable programcode operable to cause the computer to add a predetermined incrementvalue to the speed integral value at a point in time if it has beendecided that the value of the segment length exceeds the predeterminedvalue; computer readable program code operable to cause the computer todecide whether or not a sum of the speed integral value and thepredetermined increment value exceeds a predetermined threshold value;and computer readable program code operable to cause the computer togenerate a start signal for starting the passenger protection system ifit has been decided that the speed integral value exceeds thepredetermined threshold value.
 8. A computer program according to claim7 , wherein the predetermined value is a segment length of change in anintegral value in a predetermined range of another speed integral value,the another speed integral value being derived from an integral of timeof deceleration of the vehicle in a low speed crash, relative to theelapsed time.